FR2531611A1 - MEMBRANE CONTAINING A LIQUID ACTIVE SUBSTANCE AND METHOD FOR THE PREPARATION THEREOF - Google Patents

Abstract

A POLYMERIC MEMBRANE CONTAINING A LIQUID ACTIVE SUBSTANCE CONSTITUTES OF A POLYMERIC CELL LAYER CONTAINING NUMEROUS TINY CLOSED CELLS WITH THEIR WALLS AND A DENSE THIN LAYER COVERING THE SURFACE OF THE LIQUID CELL LAYER, AND THE MINUTE CELL LAYER INTO THE CELL , BY DISSOLVING A POLYMER AND THE ACTIVE LIQUID SUBSTANCE IN AN ORGANIC SOLVENT, THE ACTIVE SUBSTANCE HAS A LIMITED SOLUBILITY IN THE POLYMER AT NORMAL TEMPERATURE AND THE ORGANIC SOLVENT IS CAPABLE OF DISSOLVING THE ACTIVE SUBSTANCE AND THE POLYMER AND IS MORE VOLATILE THAN THE ACTIVE SUBSTANCE , WE APPLY THE SOLUTION TO THE SURFACE OF A SUPPORT AND EVAPORATE THE SOLVENT.

Description

The present invention relates to a membrane containing a

  liquid active substance and a process for its preparation The mem-

  brane can advantageously be used to release a liquid active substance such as a pheromone or a pesticide at a controlled and almost constant rate for a long time.

  There are already several known articles used to liberate

  Controlling an active substance These articles usually consist of a support layer and a control layer, as described for example in US Pat. No. 4,160,335 The support layer contains a active substance in the dissolved state The control layer which covers the support layer, controls the permeation or diffusion of the active substance so that the latter is released into the atmosphere

  surrounding at almost constant speed When the sub-

  active stance is liquid, the support layer is prepared by uniform dissolution of the active substance in a polymer miscible with the latter The support layer is then covered with the control layer consisting of a less miscible polymer with

the active substance.

  However, these articles have drawbacks in that the solubility of the active substance in the polymer used in the support layer is limited. Thus, it is usually difficult to obtain a support layer containing more than 30% by weight of the active substance. When a liquid active substance is dissolved in the polymer at a concentration greater than 30% by weight, the polymer can no longer form a solid gangue In fact, the content of active substance in these articles is usually limited to

about 10% by weight.

  In order to overcome this drawback, a support layer composed of a porous polymeric cell membrane was used.

  open and an active substance absorbed into the membrane -

  This support layer has a drawback: its surface is moistened by the active substance which makes it difficult

  the application of a control layer As a result, we usually include

  the supporting layer in a membrane body which serves as a control layer but the use of a membrane body presents

  disadvantages because it requires additional operating stages

  Preparations that increase the price of these items.

  The present invention relates to a membrane which

  holds a liquid active substance and allows this active substance to be released at an almost constant and controlled rate,

  as well as a process for its preparation.

  Other objects and advantages of the invention will become apparent

  on reading the description below.

  These aims and advantages have been achieved in an anisotropic structure membrane which is characterized in that it comprises

  (a) a cell layer containing countless tiny cells

  closed cells and their walls and (b) a thin dense layer covered

  covering the surface of the cell layer, the cell layer and

  the dense and thin layer together forming the control layer.

  The invention also includes a process for preparing this membrane, which process is characterized in that (1) a polymer and a liquid active substance are dissolved in an organic solvent, the liquid active substance having a limited solubility in the polymer at temperature normal, and the organic solvent being capable of dissolving both the liquid active substance and the polymer and being more volatile than the liquid active substance; (2) applying the solution obtained to the surface of a support; and (3) the solvent is evaporated from the solution> thus forming a polymeric cellular layer containing innumerable cells

  closed tiny and their walls and a thin dense layer overlaid

  covering the surface of the cell layer, tiny cells

  containing the active substance liquid.

  Other characteristics and advantages of the invention

  will emerge more clearly from the detailed description given

  below with reference to the figures of the accompanying drawings, in which

  Figures 1 and 2 are micro photographs.

  Scope Rectronic (at 1300 magnification) of a trans-

  side of the membrane according to the invention These photomicrographs were taken after complete release of the active substance

liquid contained in the membrane.

  Figures 3 to 9 are graphs showing the rate of release of a liquid active substance from the

membrane according to the invention.

  The membrane according to the invention containing a liquid active substance has an anisotropic structure including (1) a polymeric cell layer containing innumerable tiny cells

  independent and their walls and (b) a thin dense layer covered

  on the surface of the cell layer Tiny cells contain a liquid active substance that has limited solubility

  in the polymer at normal temperature.

  The liquid active substance used in the invention

  may consist of any liquid at normal temperature possessed

  during a chemical or physiological activity, for example an activity

  pesticidal activity, an attractive activity, a repellent activity and an aromatic activity. Examples of such active substances are: (pesticides like Naled, Diazinon and Sumithion; (b) fungicides like lafi-propiolactone; (c) repellents like the monohexyl ether of triethylineglycol and

  N, N-diethyl-m-toluamide; (d) attractive substances such as -

  dodecyl acetate, Z-11-tetradecenyl acetate and Z-11-

  hexadecenal; and (e) aromatic substances such as limonene and benzyl alcohol and esters, ethers and aldehydes derived therefrom.

of C 6 -C 16 hydrocarbons.

  The membrane according to the invention containing a liquid active substance has an anisotropic structure in that it carries on the surface a thin and dense layer integrally supported on a

  cell layer containing countless minus closed cells

  cells and their walls The dimension of cells ranges from 0.5 to 20%.

  The cells are separated by a thin wall of thickness 0.1 to P The liquid active substance is contained in the cells

lowercase.

  The thickness of the membrane is not particularly limited but it is usually 10 to 500 Po. The membrane according to the invention can contain an extremely high number of tiny closed cells and can thus contain up to 70% by weight approximately d liquid active substance The dense and thin layer usually has a thickness of 0.1 to 200 and preferably

from 1 to 100.

  According to the invention, the liquid active substance which must be contained in the membrane must have a limited solubility in the polymer which constitutes the membrane. The solubility in question is the maximum quantity, in parts by weight, of the liquid active substance which can dissolve in 100 parts by weight of the polymer When we speak of limited solubility we mean by this that the active substance dissolves in an amount less than parts by weight in 100 parts by weight of the polymer A preferred polymer is capable of solubilizing the substance active in quantity

from 0.01 to 1% by weight.

  The nature of the polymer can be chosen according to

  the nature of the liquid active substance Among the polymers used

  sands include polysulfones, polyether sulfones, polycarbonates, polystyrene, polymethyl methacrylate and other polyacrylic and polymethacrylic esters, polyamides, polyvinylidene chloride, polyvinylidene fluoride, cellulose esters, cellulose regenerated, polyurethanes, polyvinyl alcohol, polyvinyl chloride, acetate

  polyvinyl, polyaryl esters, acrylonitrile copolymers-

  styrene, acrylonitrile -styrene-butadiene copolymers, ethylene-vinyl acetate copolymers, chloride chloride copolymers

  vinyl-vinyl acetate and polystyrene block copolymers-

  polybutadiene The polymers can be used individually or in

combination between them.

  The membrane in question, containing a liquid substance, is prepared in the following manner. A polymer and an active substance which is liquid at normal temperature and have limited solubility in the polymer are dissolved in an organic solvent which dissolves both the substance.

  active and the polymer and is more volatile than the active substance.

  The solution obtained is applied to the surface of a support and the solvent is allowed to evaporate, thus forming a polymeric cellular layer containing innumerable tiny closed cells and their walls, and a thin dense layer covering the surface of the layer.

  cell, the tiny cells inside containing the subs-

active liquid tance.

  The organic solvent used in the invention must dissolve both the active substance and the polymer and it must be more volatile or have a lower boiling point than the active substance. The nature of the organic solvent can be chosen correctly depending on the nature of the active substance and the nature of the polymer Among the organic solvents which can be used, mention will be made of methylene chloride, chloroform, carbon tetrachloride and other halogenated aliphatic hydrocarbons; methanol, ethanol and other lower aliphatic alcohols and their acetates; acetonitrile, acetone, ethyl ether and tetrahydrofuran Organic solvents can be used

  individually or in combination with one another Organic solvents pre-

  fairies are the lower halogenated aliphatic hydrocarbons like

methylene chloride.

  In accordance with the invention, a liquid active substance and a polymer are dissolved in an organic solvent as described above. The solution is applied to a support such as paper, a sheet of plastic material, a nonwoven fabric, a metallic foil or laminate of these materials and allowed to completely evaporate The total concentration of the liquid active substance and the polymer in the solution is usually

  to 40% by weight and preferably from 15 to 30% by weight.

  The organic solvent can be evaporated at temperature

  normal or hot when necessary.

  Because the liquid active substance has limited solubility in the polymer, phase separation occurs between the active substance and the polymer as the solvent

  organic evaporates so tiny droplets of the sub-

  active stance disperses evenly through the polymer matrix.

  As a result, the polymer forms innumerable tiny closed cells containing the liquid active substance. As the evaporation of the solvent progresses, the concentration of the polymer increases on the surface of the applied solution and eventually a layer is formed. dense dense integrated into the cell layer

  itself formed of tiny cells.

  The tiny cells formed in the membrane are separated by walls with a thickness of 0.1 to 10 µm. The size of the cells is approximately 0.5 to 20 µm. Thus, the membrane contains 80% cells and it can contain up to about 70% by weight of a liquid active substance However, the content of

  liquid active substance is preferably about 50% by weight.

  Because the liquid active substance has limited solubility in the polymer and is covered with a thin dense layer, it diffuses small cells into the polymer at a limited speed and is released into the atmosphere at an almost constant speed by the surface of the thin and dense layer Thus, the membrane according to the invention is used to release a substance

  activates slowly and at controlled speed.

  The examples which follow illustrate the invention without however limiting its scope; in these examples, the indications of parts and percentages are by weight unless otherwise stated.

EXAMPLE 1

  1 ml of Z-ll-hexadecenal, an attractive substance for insects, and 1 g of polysulfone are dissolved in 10 ml of methylene chloride. This solution is applied at temperature.

  ambient on a support consisting of a composite paper sheet-

  aluminum The methylene chloride is allowed to evaporate at room temperature.

  ambient ture This gives a 40-day-thick membrane

  containing approximately 50% of the attractive substance.

  When all the latter has been released, we examine

  the cross section of the membrane under the electron microscope.

  A photograph under this microscope (at 1,300 magnification) is

  shown in Figure 1 of the accompanying drawings.

  In the same way, using Z-letetradecenyl acetate, another insect-attractive substance instead of Z-ll-hexadecenal, a 40 p thick membrane was formed.

  containing about 50% Z-11-tetradecenyl acetate.

  When all the attractive substance has been released, the cross section of the membrane has been examined with an electron microscope. A photograph taken with this microscope (at 1300 magnification) is shown in FIG. 2 of the accompanying drawings. These photographs under the electron microscope show that the tiny cells contained in the membrane have dimensions from 1 to 5 A, their walls have a thickness of 0.2 to 0.5 ï, and the thin and dense layer covering the membrane has a thickness of 4 ï.

  The solubility as defined above of Z-ll-hexa-

  decenal and Z-ll-tetradecenyl acetate in polysulfone

  is 0.7 part by weight and 0.8 part by weight respectively.

EXAMPLE 2

  1 ml of dodecyl acetate, an attractive substance for insects, and 1 g of polysulfone are dissolved in 10 ml of methylene chloride. The solution is applied to a film of

  support at room temperature The methyl chloride is evaporated

  lene at rest at room temperature This gives membranes

  of varying thicknesses containing about 50% of the attracting substance

  The thicknesses of the membranes are 109 20 and 40.

  The speed of release of the attractive substance at 250 ° C. is determined by the reduction in weight of the membrane. The results obtained are plotted graphically in FIG. 3 of the accompanying drawings. This graph shows that the speed of release per unit area of the membrane remains practically constant but

  that the thicker the membrane, the longer the release time

  ration. On the other hand, when membranes are prepared by varying the content of the attractive substance from 30 to 70%, it is observed that the rate of release of the attractive substance is all the more

  higher than the content of attractive substance is higher.

  This example shows that the duration of release of an active substance can be controlled by appropriate modification of the thickness of the membrane. It is also possible to control the speed of

  release of an active substance by varying the content of

active tance in the membrane.

EXAMPLE 3

  Various amounts (1 ml, 0.5 ml, 0.2 ml and 0.1 ml) of Z-ll-tetradecenyl acetate and 1 g of polysulfone are dissolved in ml of methylene chloride. The solution is applied to a support film at room temperature and the solvent is evaporated. Four membranes, approximately 80 m thick, are thus formed.

  containing approximately 50%, 33%, 17% and 9% of the pheromone, respectively.

  The dense and thin layer formed on the surface of the membrane obtained has a thickness inversely proportional to the content of the pheromone,

  that is, it is about 8 ô, 20), 4 U ï and 70 ô.

  The rate of release of the pheromone at 25 ° C. is determined by measuring the weight loss of the membrane and by quantitative analysis of the residual pheromone contained in the membrane. The results shown graphically in FIG. 4 of the accompanying drawings show that the release of the pheromone occurs at almost constant speed for 100 days, but the slower the layer

dense and thin is thicker.

EXAMPLE 4

  1 ml of Z-11-tetradecenyl acetate and 1 g of polysulfone, polycarbonate or polymethyl methacrylate are dissolved in ml of methylene chloride. The solution obtained is applied to a support film at room temperature and the mixture is allowed to evaporate. solvent There are thus obtained three membranes approximately 40 p thick containing approximately 50% of the pheromone The solubility of Z-11-tetradecenyl acetate in the three polymers mentioned is located in

  the range of 0.2 to 0.8 parts by weight.

  The rate of release of the pheromone at C is determined by measuring the weight loss of the membrane. The results shown graphically in FIG. 5 of the appended drawings show that the rate of release is practically the same for the three membranes and that the release of the pheromone continues for

days.

EXAMPLE 5

  1 ml of Z-11-tetradecenyl acetate and 1 g of cellulose triacetate are dissolved in 10 ml of methylene chloride. The solution is applied to a support film at room temperature and the solvent is evaporated, a membrane is thus obtained. p of thickness containing about 50% of the pheromone The solubility of Z-ll-tetradecgnyl acetate in cellulose triacetate

  is of the order of 1.6 to 1.8 parts by weight.

  The rate of release of the pheromone at 250 ° C. is determined by measuring the weight loss of the membrane. The results shown graphically in FIG. 6 of the appended drawings show

  that the rate of release is almost constant for 40 days.

EXAMPLE 6

  By operating as described in Example 1, a polysulfone membrane 40, p thick containing about 50% is prepared.

of Z-11-hexadecenal.

  We measure the speed of release of the substance

  attractive at 250 C as described in Example 1.

  Because the attractive substance used in this

  example is an aldehyde, it is chemically unstable and is

  slightly oxidized by oxidizing agents and / or ultraviolet light,

  Therefore, it is difficult to control the release rate.

  However, the results obtained in this example and represented graphically-

  ment in Figure 7 of the accompanying drawings show that the substance

  attractive is released at almost constant speed for 30 days.

EXAMPLE 7

  1 ml of the insecticides Naled, Diazinon or

  Sumithion and 1 g of polycarbonate in 10 ml of methylene chloride.

  By the procedure of Example 1, three membranes are formed

  about 40 feet thick containing about 50% insecticide.

  The rate of release of the insecticide at 250 ° C. is measured by extracting the residual insecticide contained in the membrane by

  ethanol after a certain time The results represented graphi-

  Only in Figure 8 of the accompanying drawings show that the insecti-

  cide is released at almost constant speed for a period of time

  longed. When used against Bluttela germanica as described below, the membranes prepared in this example show insecticidal activity for a prolonged period. The membrane containing Naled is effective for more than 150 days. This insecticide activity is demonstrated in the following manner: A 9 cm diameter membrane containing the insecticide is placed in a round plastic container. Ten adult individuals are placed in the container. Bluttela germanica We measure

  the time it takes for 50% of the insects to fall unconscious.

  The duration during which this time remains almost constant (approximately 5 hours in the case of the Naled) is considered to be effective service time.

i 5 EXAMPLE 8

  Dissolve 1 ml of monohexyl ether of triethylene-

  glycol, an insect repellent, and 1 g of polycarbonate in 10 ml of methylene chloride By operating as described in Example 1, a 40-day thick membrane is formed containing approximately 50% of

repellant.

  The rate of release of the repellant is measured as described in Example 1 The results shown graphically in FIG. 9 of the accompanying drawings show that the repellant is

  released at almost constant speed for 30 days.

  When this membrane is used against Bluttela germa-

  nica as described below, we see that 90% of the repellent effect

  of the membrane persist for one month.

  The repellency is determined as follows: A closed container 500 mm wide, 400 mm deep and 150 mm high is used as the test container. In the center of the left edge of this container, place a refuge At the rear edge of the right edge of the container, a cockroach trap ("Rotel" from the firm Fumakilla Limited) is placed in the form of a 2 cm wide tape stuck on the ground On the front edge from the right edge of the container, another cockroach trap of the same type is placed, containing a bait. A hundred adult Bluttela germanica individuals are placed in the refuge, who have been subjected to photoperiodic control and have been deprived of food for three days. light, we open the refuge door and 2.5 hours later, we count the cockroaches that have entered each of the traps. The repulsion ratio is calculated from the following equation Repulsion ratio,% = / ZC-R) / (C + R) 7 x 100 in which C is the number of cockroaches caught in the control trap (this is i.e. in the absence of the membrane) and R is the number of

  cockroaches caught using a repellant.

  It is clear that the invention is in no way limited to the embodiments described above by way of examples and that a person skilled in the art can make modifications without thereby

get out of its frame.

Claims (6)

  1 Membrane containing a liquid active substance, with struc-   anisotropic structure, characterized in that it comprises (a) a layer   polymer cell containing countless minus closed cells   cells and their walls and (b) a thin, dense layer covering the surface of the cell layer, the tiny cells containing a liquid active substance having limited solubility in the polymer   in question at normal temperature.   -2 Membrane according to claim 1, characterized in that the side of the cell layer of the membrane is supported on a support.   3 membrane according to claim 1, characterized in that the tiny cells of the cell layer have a diameter of 0.5 to 20 1 and their walls have a thickness of 0.1 to 10 4 membrane according to claim 1, characterized in that that the thin and dense layer has a thickness of 0.1 to 100 membrane according to claim 1, characterized in that the limited solubility of the liquid active substance in the polymer is less than 5 parts by weight per 100 parts in weight of the polymer.   6 Membrane according to claim 5, characterized in that the limited solubility of the liquid active substance in the polymer is 0.01 to 2 parts by weight per 100 parts by weight of the polymer. 7 membrane according to claim 1, characterized in that the polymer is chosen from the group formed by polysulfone, polyether sulfones, polycarbonates, polystyrene, polyacrylic and polymethacrylic esters, polyamides, polyvinylidene chloride, fluoride polyvinylidene, cellulose esters, regenerated cellulose, polyurethanes, polyvinyl alcohol, polyvinyl chloride, polyvinyl acetate, polyaryl esters, acrylonitrile-styrene copolymers, acrylonitrile styrene-butadiene copolymers, ethylene copolymers -vinyl acetate, vinyl chloride-acetate copolymers   vinyl and polystyrene-polybutadiene block copolymers.   8 Membrane according to claim 1, characterized in that the liquid active substance is a liquid substance at temperature   normal with chemical or physiological activity.   9 membrane according to claim 1, characterized in that the chemical or physiological activity is a pesticidal activity,   an attractive activity or an aromatic activity.   Process for the preparation of a membrane containing a   liquid active substance according to any one of claims 1   to 9, characterized in that (1) a polymer and a liquid active substance are dissolved in an organic solvent, the liquid active substance having limited solubility in said polymer at normal temperature and   the organic solvent being capable of solubilizing both the substance   this liquid active and the polymer and being more volatile than said liquid active substance (2) the solution obtained is applied to the surface of a support; and (3) the solvent is evaporated from the solution, thereby forming a polymeric cell layer containing countless tiny closed cells and their walls and a thin, dense layer   covering the surface of the cell layer, tiny cells   cules containing the liquid active substance inside.   I 1, Method according to claim 10, characterized in that the organic solvent is chosen from the group formed by   lower halogenated aliphatic hydrocarbons, alcohols   lower phatics and their acetic esters, acetonitrile,   acetone, diethyl ether and tetrahydrofuran.   12 Method according to claim 10 or l, characterized in that the solvent is a halogenated aliphatic hydrocarbon inferior.